rust v1.0.0A

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---
name: "rust"
description: 'Build safe, concurrent, and performant systems with Rust. Use when writing Rust applications, implementing ownership and borrowing patterns, building concurrent code with threads/async, designing trait-based abstractions, or optimizing Rust performance.'
metadata:
 author: "Frontier"
 version: "1.0.0"
 created: "2025-01-15"
 updated: "2025-01-15"
compatibility:
 languages: ["rust"]
 platforms: ["windows", "linux", "macos"]
---

# Rust Development

> **Purpose**: Best practices for Rust development including ownership, error handling, concurrency, and safety patterns.

---

## When to Use This Skill

- Building Rust applications and systems
- Working with ownership, borrowing, and lifetimes
- Implementing error handling with Result and Option types
- Writing concurrent code with threads and async
- Designing trait-based abstractions

## Decision Tree

```
Rust Project Decision
+-- Building a CLI tool?
|   +-- Argument parsing? -> clap
|   +-- Pretty output? -> anyhow + color-eyre
+-- Building a web service?
|   +-- Async HTTP? -> axum or actix-web
|   +-- Need middleware? -> tower (used by axum)
+-- Error handling strategy?
|   +-- Library code? -> thiserror (typed errors)
|   +-- Application code? -> anyhow (ergonomic errors)
+-- Async runtime?
|   +-- General purpose? -> tokio
|   +-- Lightweight? -> smol or async-std
+-- Serialization needed? -> serde + serde_json / serde_yaml
+-- Performance-critical path? -> Benchmark with criterion before optimizing
```

## Prerequisites

- Rust 1.94+ installed via rustup
- Cargo package manager

## Table of Contents

1. [Project Structure](#project-structure)
2. [Ownership and Borrowing](#ownership-and-borrowing)
3. [Error Handling](#error-handling)
4. [Traits and Generics](#traits-and-generics)
5. [Concurrency](#concurrency)
6. [Testing](#testing)
7. [Performance](#performance)
8. [Security](#security)
9. [Best Practices](#best-practices)

---

## Project Structure

### Standard Layout

```
project/
+-- src/
| +-- main.rs # Binary entry point
| +-- lib.rs # Library root
| +-- config.rs # Configuration
| +-- error.rs # Error types
| +-- models/
| | +-- mod.rs
| | -- user.rs
| -- services/
| +-- mod.rs
| -- user_service.rs
+-- tests/
| -- integration_tests.rs
+-- benches/
| -- benchmarks.rs
+-- examples/
| -- basic_usage.rs
+-- Cargo.toml
+-- Cargo.lock
-- README.md
```

### Cargo.toml

```toml
[package]
name = "myapp"
version = "0.1.0"
edition = "2021"
authors = ["Your Name <you@example.com>"]
description = "A brief description"

[dependencies]
tokio = { version = "1", features = ["full"] }
serde = { version = "1", features = ["derive"] }
thiserror = "1"
anyhow = "1"

[dev-dependencies]
tokio-test = "0.4"

[profile.release]
lto = true
opt-level = 3
```

---

## Core Rules

### [PASS] DO

- Use `clippy` for linting: `cargo clippy`
- Format with `rustfmt`: `cargo fmt`
- Prefer `&str` over `String` for function parameters
- Use `#[derive]` for common traits
- Write documentation with `///`
- Use `Result` for recoverable errors
- Leverage the type system for safety

### [FAIL] DON'T

- Use `unwrap()` in production code
- Ignore compiler warnings
- Use `unsafe` without clear justification
- Clone unnecessarily
- Write overly complex lifetimes
- Panic for expected error conditions

---

## Anti-Patterns

- **Unwrap in Production**: Using `.unwrap()` or `.expect()` in non-test code -> Use `?` operator with proper error types
- **Unnecessary Cloning**: Cloning data to satisfy the borrow checker -> Refactor ownership or use references and lifetimes
- **Unsafe Without Justification**: Using `unsafe` blocks without documented safety invariants -> Avoid unsafe; if required, add `// SAFETY:` comments
- **Stringly Typed APIs**: Passing `String` where an enum or newtype fits -> Use the type system to encode valid states
- **Blocking in Async**: Calling blocking I/O inside async functions -> Use `tokio::task::spawn_blocking` for blocking work
- **Ignoring Clippy Warnings**: Suppressing clippy lints without reason -> Fix the issue or document why the lint is suppressed

---

## References

- [The Rust Book](https://doc.rust-lang.org/book/)
- [Rust by Example](https://doc.rust-lang.org/rust-by-example/)
- [Rust API Guidelines](https://rust-lang.github.io/api-guidelines/)
- [Tokio Tutorial](https://tokio.rs/tokio/tutorial)

---

**Version**: 1.0
**Last Updated**: February 5, 2026

## Troubleshooting

| Issue | Solution |
|-------|----------|
| Borrow checker errors | Use .clone() for simple cases, refactor with owned types or Arc<Mutex<T>> |
| Lifetime annotation confusion | Start with owned types, add references only when performance requires it |
| Async runtime errors | Ensure using #[tokio::main] or equivalent, dont mix sync and async without spawn_blocking |